Abstract
The origin of high-temperature superconductivity in iron-based superconductors is still not understood; determination of the pairing symmetry is essential for understanding the superconductivity mechanism. In the iron-based superconductors that have hole pockets around the Brillouin zone centre and electron pockets around the zone corners, the pairing symmetry is generally considered to be s±, which indicates a sign change in the superconducting gap between the hole and electron pockets. For the iron-based superconductors with only hole pockets, however, a couple of pairing scenarios have been proposed, but the exact symmetry is still controversial. Here we determine that the pairing symmetry in KFe2As2—which is a prototypical iron-based superconductor with hole pockets both around the zone centre and around the zone corners—is also of the s± type. Our laser-based angle-resolved photoemission measurements have determined the superconducting gap distribution and identified the locations of the gap nodes on all the Fermi surfaces around the zone centres and the zone corners. These results unify the pairing symmetry in hole-doped iron-based superconductors and point to spin fluctuation as the pairing glue in generating superconductivity.
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Data availability
All raw data generated during the study are available from the corresponding authors upon request. Source data are provided with this paper.
Code availability
The codes used for the fitting and simulation process in this study are available from the corresponding authors upon request.
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Acknowledgements
This work is supported by: the National Key Research and Development Program of China (grant nos. 2021YFA1401800 (to X.J.Z.), 2017YFA0302900 (to H.Q.M.), 2018YFA0704200 (to H.Q.M.), 2018YFA0305600 (to G.D.L.), 2019YFA0308000 (to H.Q.M.) and 2022YFA1604203 (to L.Z.)); the National Natural Science Foundation of China (grant nos. 11888101 (to X.J.Z.), 11922414 (to L.Z.) and 11974404 (to G.D.L.)); the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (grant nos. XDB25000000 (to X.J.Z.) and XDB33000000 (to H.Q.M.)); the Innovation Program for Quantum Science and Technology (grant no. 2021ZD0301800 (to X.J.Z.)); the Youth Innovation Promotion Association of CAS (grant nos. Y2021006 (to L.Z.) and Y202001 (to H.Q.L.)); and the Synergetic Extreme Condition User Facility (SECUF) (to X.J.Z.). We thank the MAX IV Laboratory for time on Beamline Bloch under Proposal 20221180. Research conducted at MAX IV, a Swedish national user facility, was supported by the Swedish Research council under contract 2018-07152, the Swedish Governmental Agency for Innovation Systems under contract 2018-04969 and Formas under contract 2019-02496. We thank C. Polley and B. Thiagarajan at Beamline Bloch of MAX IV for supporting the beamtime.
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X.J.Z., L.Z. and D.S.W. proposed and designed the research. D.S.W., W.S.H., Y.J.S., H.Q.L. and S.L.L. contributed to the sample growth and the magnetic and resistivity measurements. J.J.J., J.G.Y., H.T.Y., H.T.R., P.A., X.Z., C.H.Y., T.M.M., C.L.L., S.J.Z., F.F.Z., F.Y., Z.M.W., N.Z., L.J.L., R.K.L., X.Y.W., Q.J.P., H.Q.M., G.D.L., Z.Y.X., L.Z. and X.J.Z. contributed to the development and maintenance of the ARPES systems and related software development. D.S.W. carried out the ARPES experiment with J.J.J., J.G.Y., J.Y.L., H.K.C., Y.H.Y., C.P., Y.L.C., L.Z. and X.J.Z. D.S.W., L.Z. and X.J.Z. analysed the data. X.X.W. contributed to the band structure calculations. X.J.Z., L.Z. and D.S.W. wrote the paper. All authors participated in discussion and commented on the paper.
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Wu, D., Jia, J., Yang, J. et al. Nodal s± pairing symmetry in an iron-based superconductor with only hole pockets. Nat. Phys. 20, 571–578 (2024). https://doi.org/10.1038/s41567-023-02348-1
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DOI: https://doi.org/10.1038/s41567-023-02348-1
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